Don't make it so obvious you really didn't want to be there!
I popped into my local co op on my way home from work to get a couple of things. There was quite a queue and when I got to be served by a young guy, I was gobsmacked.
Considering he was serving customers, he could not have tried any more harder to look as miserable as possible and make it pretty obvious he did not want to be at work and serving people! His whole body language was that he did not want to be there, I was quite shocked as I never been served by someone that has looked so unprofessional. I even had to ask for a bag for my shopping and he had about as much enthusiasm as a dead fish.
I really wanted to say to him for god's sake don't make it so obvious you don't want to be here.